In cooperative operation of plural robots such that plural robot-manipulators grip a workpiece and move it, the plural robot manipulators need to be operated so as to maintain relative positions to each other. Hitherto, there have been methods for teaching such operations as described hereafter.
A first method is off-line teaching, wherein operating positions of the robot are inputted as data values into a computer and are set in teaching. However, this method becomes difficult, and subsequently unfavorable, as the accuracy of the operating positions of the robots with respect to their actual work is not necessarily superior.
A second method is to manually operate the robot to a moving position of an actual operation using a teaching box, and to teach the operating position of the robot by sensing and storing the position and orientation of the robot at that time. In this method, it is very difficult to teach each of the plural robots, by manual operation, a position and orientation which actually maintains a relative position, including orientation, of a terminal hand. Accordingly, this method has often been used by teaching only a starting position to plural robots performing a cooperative operation. Subsequent positions of one of the plural robots are then taught in regard to subsequent teaching positions in the cooperative operation. As such, the plural robots are operated in a manner so that an original relative position is maintained with respect to the operating path of the robot which is taught by the above-mentioned method. An example of this method is shown in FIG. 2. In this example, operating positions and orientations P1, P2, P3, P4 of a first robot manipulator, and an operating position and orientation Q1 of a second robot manipulator, corresponding to P1, are taught. Operating positions and orientations Q2, Q3, Q4 are then determined by calculation from a relative position of P1 and Q1 and P2, P3, P4, and operational paths of respective manipulators are interpolated. As the position is detected and memorized by manually operating the robot to an actual operating position, a teaching accuracy in this method is better. Yet, when the robot operation requires a gripping of a workpiece, complications arise. While a gripping position of a workpiece can be accurately taught, an accurate teaching of the movement of a workpiece by robot manipulators is not realized as all of the operating positions are directed at the robot manipulators.
Further, a detailed teaching of a gripping position of a workpiece can be difficult. In teaching an operating case where, based upon a gripping position of one robot manipulator, a large workpiece is gripped and moved with two robot manipulators, a slight difference in gripping orientation during the teaching operation can become a large positional difference at the other end of the work process. As demonstrated in FIG.17, such a situation is liable to become a problem in the operation of the robot manipulator which grips the other end of the workpiece.